A Solar Sentinel's Stunning Debut

Solar prominence on March 30, 2010
Twisting streamers of ionized gas tower over the Sun in a large prominence captured by the Solar Dynamics Observatory on March 30, 2010.

A Solar Sentinel's Stunning Debut

When NASA's Solar Dynamics Observatory roared into space on February 11th, mission scientists breathed a sign of relief. Launch is (almost) always the riskiest part of any space mission.


Solar Dynamics Observatory
Three instruments aboard NASA's Solar Dynamics Observatory will keep the Sun under constant scrutiny throughout an 11-year-long solar cycle.

Once SDO safely reached its final orbit, a geosynchronous circle inclined 28° to the equator, the flight team got to work readying the craft to monitor the Sun as never before. Commands beamed up and data beamed down through the mission's dedicated ground station in New Mexico.

(Just to clarify, an orbit that's geosynchronous has a 24-hour period, matching Earth's rotation; if a spacecraft's orbit is geosynchronous and circular, from the ground the craft appears to nod up and down in declination but keeps the same right ascension. A geostationary orbit has, in addition, 0° inclination — telecommunications satellites use such orbits because they appear fixed in the sky, so that receiving antennas don't need to track them.)

After two months of waiting, we've finally gotten a glimpse of what SDO can do. Yesterday afternoon NASA officials unveiled the first images and videos from the craft's three instruments.

The Sun's disk has always fascinated me in a kaleidoscopic way. Seething and churning, its surface is constantly changing. Anyone who's kept tabs on the Solar and Heliospheric Observatory (SOHO) knows what I mean. But SDO takes the visualization of the Sun to a whole new level. The frequency, or cadence, of the observations is much faster, and the videos released yesterday are breathtaking. They're too big to show here — the little clip you can view at right is just a tease, really. To get a real eyeful, head over to the project's special website set up for these first-light releases. (The mission's main website is here.)

Simply put, SDO's 5-year mission is to characterize how the Sun changes and how those changes affect Earth. It's not the first spacecraft with that objective, but the three experiments aboard are designed to identify those changes as never before. Each day the craft will transmit some 1½ terabytes of data — the equivalent of 380 full-length movies.


Full-disk view of erupting Sun
This false-color image, produced by combining three images from the Solar Dynamics Observatory's AIA instrument, shows the Sun's appearance on April 8, 2010.

I think the instrument you'll get to know best is the Atmospheric Imaging Assembly (AIA), a quartet of telescopes that record full-disk images at ultraviolet and extreme-ultraviolet wavelengths. Whereas SOHO takes images at some of these same wavelengths every few minutes, the AIA imagers will snap away every 10 seconds.

SDO's Extreme Ultraviolet Variability Experiment (EVE) will focus on the solar photons that primarily heat Earth's upper atmosphere and create our ionosphere. Other spacecraft have measured the Sun's extreme-ultraviolet variability, but EVE will do it better and faster, in some cases sampling the Sun's output every ¼ second.

The job of SDO's Helioseismic and Magnetic Imager (HMI) is to monitor the magnetic fields at the solar surface and to probe the goings-on deeper down. Our star is constantly quivering, and physicists can use the strength and frequency of these vibrations to map the Sun's interior — in much the same way that geophysicists use earthquakes to probe Earth's mantle and core.

It's great that solar scientists now have a powerful new tool to explore our star. But I'm equally thrilled that the spacecraft will be producing some gorgeous eye candy to captivate and engage the public.